FIELD OF THE INVENTION
This invention relates to a method of molding a thin hollow product of polysilazane which is a precursor of a ceramic of silicon nitride or a mixture of silicon nitride and silicon carbide.
Polysilazane is a polymer composed of silicon, nitrogen and hydrogen occasionally containing carbon, and is obtained as a liquid having a molecular weight of 200 to 800 immediately after synthesis. The liquid polysilazane is converted to a solid by heating.
In the case of an inorganic polysilazane (H.sub.2 SiNH).sub.n, when the heating temperature is gradually elevated, pyrolysis of the solid polysilazane begins around 150.degree. C. and usually finishes around 600.degree. C. The pyrolysis product is amorphous silicon nitride. However, a sintered body composed of .alpha.-silicon nitride and metal silicon is obtained by heating at a temperature of 1,000.degree. to 1,800.degree. C. at ordinary pressure in an inert atmosphere. When the heating is conducted in a nitrogen gas atmosphere, the sintered body obtained is a single phase of .alpha.-silicon nitride. A sintered body composed of silicon nitride and silicon carbide is obtained from (CH.sub.3 SiHNH).sub.n through a similar treatment.
Incidentally, polysilazane has been noticed as a raw material of ceramics comparatively recently, and no reference has been found disclosing a molding method for polysilazane.